Comprehensive Understanding of Reduction Mechanisms of ... · Comprehensive Understanding of...

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Comprehensive Understanding of Reduction Mechanisms of Ethylene Sulte in EC-Based Lithium-Ion Batteries Fucheng Ren, Wenhua Zuo, Xuerui Yang, Min Lin, Liangfan Xu, Wengao Zhao, Shiyao Zheng, and Yong Yang* ,,College of Energy and State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China * S Supporting Information ABSTRACT: The reliable electrolyte additives are critically important to satisfy the rapidly increasing demand for electrical energy storage with safety, low cost, long life, and high-energy/ power density. As an eective electrolyte additive, ethylene sulte (ES) is widely used in lithium-ion batteries to improve their cycling performance at low temperature. However, its working mechanism, particularly in ethylene carbonate (EC)- based electrolyte, is still elusive. Here, we present a comprehensive theoretical study of the reduction mechanism of ES in EC-based electrolyte with the ring-opening reaction followed by dimerization reaction and/or the second-electron reduction path. The eects of participation of cosolvents such as diethyl carbonate (DMC), ethyl methyl carbonate (EMC), and dimethyl sulte (DMS) on the ring-opening reaction process of ES were also carefully investigated. Based on our calculation results, the reactivity order of the clusters (ES)Li + (M) (M = EC, PC, VC, DMC, DMS, and EMC) is shown as follows: (ES)Li + (VC) (4.09 × 10 55 s -1 ) > (ES)Li + (PC) (9.21 × 10 47 s -1 ) > Li + (ES) (8.47 × 10 47 s -1 ) > (ES)Li + (EC) (7.07 × 10 47 s -1 ) > (ES)Li + (DMS) (3.11 × 10 43 s -1 ) > (ES)Li + (EMC) (1.91 × 10 41 s -1 ) > (ES)Li + (DMC) (2.48 × 10 37 s -1 ). The implication of our calculation results on the formation of SEI on the graphite is also discussed. 1. INTRODUCTION Lithium-ion batteries (LIBs) oer various advantages com- pared to other rechargeable electrical energy storage systems; 1-4 thus, they have been widely applied in our daily lives such as portable electronics and electric vehicles. 5-7 However, with the rapid development of our society and technology, there comes a great demand for advanced LIBs with longer cycling life, higher safety, and higher-energy/power densities. During the working and storage of LIBs, a Li + conducted, whereas electron-insulated layer called solid electrolyte interphase (SEI) was formed on the electrode surface by the complex reactions of the electrolytes. By separating electrodes from direct contact with an electrolyte, the SEI is eective in preventing further electrolyte decomposition and ensuring continual Li + intercalation/ deintercalation. 8 As a result, the properties of SEI such as composition, uniformity, and stability directly correlate to the cycling performance and calendar life of LIBs. 9,10 Currently, EC is the most widely used electrolyte solvent in LIBs, not only because of its ability to dissolve and dissociate lithium salt but also more importantly because of its functionality to decompose and form an SEI layer on the electrode surface to protect the electrode from exfoliation in the initial charge process. 11 However, the SEI formed by EC tends to be inhomogeneous and loose, which cannot provide a good long-term protection for electrode materials. Electrolyte additives are commonly used as a simple and eective approach to form a homogeneous SEI with proper thickness and high Li + conductivity and therefore to prevent or alleviate unwanted parasitic reactions. 9,10 Organic sulfur-containing compounds such as sultes, sulfates, and sultones are generally soluble in electrolyte solvents and have been proposed as SEI- forming additives with promising performances. 12-15 The reduction potential of these additives is normally higher than that of typical solvents such as EC, PC, and DMC, and the reduction products may get incorporated into the SEI lm and thus lead to the improvements of cell performance. 9 Among the sulfur-containing compounds listed above, ethylene sulte (ES) attracted enormous amounts of attention as an outstanding lm-forming additive. 16-21 Dahn et al. 22-24 found that the introduction of ES (1 wt %) to an EC-based electrolyte could eectively improve the cycling stability of NMC/graphite pouch cells. Ota et al. 18 suggested that the SEI lm on graphite anode contains both inorganic materials like Li 2 SO 3 and organic materials like ROSO 2 Li when ES is used as an electrolyte additive. Received: December 13, 2018 Revised: February 1, 2019 Published: February 22, 2019 Article pubs.acs.org/JPCC Cite This: J. Phys. Chem. C 2019, 123, 5871-5880 © 2019 American Chemical Society 5871 DOI: 10.1021/acs.jpcc.8b12000 J. Phys. Chem. C 2019, 123, 5871-5880 Downloaded via XIAMEN UNIV on August 1, 2019 at 02:44:47 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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Page 1: Comprehensive Understanding of Reduction Mechanisms of ... · Comprehensive Understanding of Reduction Mechanisms of ... followed by dimerization reaction and/or the second-electron

Comprehensive Understanding of Reduction Mechanisms ofEthylene Sulfite in EC-Based Lithium-Ion BatteriesFucheng Ren,† Wenhua Zuo,‡ Xuerui Yang,† Min Lin,‡ Liangfan Xu,‡ Wengao Zhao,† Shiyao Zheng,‡

and Yong Yang*,†,‡

†College of Energy and ‡State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College ofChemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China

*S Supporting Information

ABSTRACT: The reliable electrolyte additives are criticallyimportant to satisfy the rapidly increasing demand for electricalenergy storage with safety, low cost, long life, and high-energy/power density. As an effective electrolyte additive, ethylenesulfite (ES) is widely used in lithium-ion batteries to improvetheir cycling performance at low temperature. However, itsworking mechanism, particularly in ethylene carbonate (EC)-based electrolyte, is still elusive. Here, we present acomprehensive theoretical study of the reduction mechanismof ES in EC-based electrolyte with the ring-opening reactionfollowed by dimerization reaction and/or the second-electronreduction path. The effects of participation of cosolvents such asdiethyl carbonate (DMC), ethyl methyl carbonate (EMC), anddimethyl sulfite (DMS) on the ring-opening reaction process of ES were also carefully investigated. Based on our calculationresults, the reactivity order of the clusters (ES)Li+(M) (M = EC, PC, VC, DMC, DMS, and EMC) is shown as follows:(ES)Li+(VC) (4.09 × 1055 s−1) > (ES)Li+(PC) (9.21 × 1047 s−1) > Li+(ES) (8.47 × 1047 s−1) > (ES)Li+(EC) (7.07 × 1047 s−1)> (ES)Li+(DMS) (3.11 × 1043 s−1) > (ES)Li+(EMC) (1.91 × 1041 s−1) > (ES)Li+(DMC) (2.48 × 1037 s−1). The implication ofour calculation results on the formation of SEI on the graphite is also discussed.

1. INTRODUCTION

Lithium-ion batteries (LIBs) offer various advantages com-pared to other rechargeable electrical energy storagesystems;1−4 thus, they have been widely applied in our dailylives such as portable electronics and electric vehicles.5−7

However, with the rapid development of our society andtechnology, there comes a great demand for advanced LIBswith longer cycling life, higher safety, and higher-energy/powerdensities. During the working and storage of LIBs, a Li+

conducted, whereas electron-insulated layer called solidelectrolyte interphase (SEI) was formed on the electrodesurface by the complex reactions of the electrolytes. Byseparating electrodes from direct contact with an electrolyte,the SEI is effective in preventing further electrolytedecomposition and ensuring continual Li+ intercalation/deintercalation.8 As a result, the properties of SEI such ascomposition, uniformity, and stability directly correlate to thecycling performance and calendar life of LIBs.9,10

Currently, EC is the most widely used electrolyte solvent inLIBs, not only because of its ability to dissolve and dissociatelithium salt but also more importantly because of itsfunctionality to decompose and form an SEI layer on theelectrode surface to protect the electrode from exfoliation inthe initial charge process.11 However, the SEI formed by ECtends to be inhomogeneous and loose, which cannot provide a

good long-term protection for electrode materials. Electrolyteadditives are commonly used as a simple and effectiveapproach to form a homogeneous SEI with proper thicknessand high Li+ conductivity and therefore to prevent or alleviateunwanted parasitic reactions.9,10 Organic sulfur-containingcompounds such as sulfites, sulfates, and sultones are generallysoluble in electrolyte solvents and have been proposed as SEI-forming additives with promising performances.12−15 Thereduction potential of these additives is normally higher thanthat of typical solvents such as EC, PC, and DMC, and thereduction products may get incorporated into the SEI film andthus lead to the improvements of cell performance.9 Amongthe sulfur-containing compounds listed above, ethylene sulfite(ES) attracted enormous amounts of attention as anoutstanding film-forming additive.16−21 Dahn et al.22−24

found that the introduction of ES (1 wt %) to an EC-basedelectrolyte could effectively improve the cycling stability ofNMC/graphite pouch cells. Ota et al.18 suggested that the SEIfilm on graphite anode contains both inorganic materials likeLi2SO3 and organic materials like ROSO2Li when ES is used asan electrolyte additive.

Received: December 13, 2018Revised: February 1, 2019Published: February 22, 2019

Article

pubs.acs.org/JPCCCite This: J. Phys. Chem. C 2019, 123, 5871−5880

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To dive deeper into the film-forming mechanisms of ES,several theoretical studies have been carried out. First, Xing etal.25 proposed a one-electron reduction mechanism in the gasphase. After that, Leggesse et al.26 studied the two-electronreduction mechanism of ES in PC-based electrolyte in vacuumand solvent. Recently, Sun et al.27 built supermolecular clusters[(ES)Li+(PC)m](PC)n (m = 1−2; n = 0, 6, and 9) toinvestigate the effect of explicit solvent molecules on the ring-opening step of ES and found that the theoretical reductionpotential of ES is in agreement with the experimental one.However, previous studies only considered the effect of PCmolecule while ignoring the effect of EC and cosolvents suchas DEC, DMC, and DMS on the ES reduction process.Furthermore, as an essential part of the SEI film formationprocess, the termination reactions of the radical anions formedby ES in electrolyte solvents are seldom reported before. As aresult, the reduction mechanisms and the possible terminationreactions of ES need further exploration and perfection to helpfurther understand the components of SEI in depth.In this paper, we present a comprehensive theoretical

calculation of ES in EC solvents with the ring-opening reactionfollowed by dimerization reaction and/or the second-electronreduction path. It is theoretically confirmed that ES can bereduced prior to EC to form a reduction precursor. The effectsof the implicit and explicit solvents on the reduction reactionof ES in EC-based electrolyte were systematically studied.Especially, the clusters (ES)Li+(M)n (M: EC, n = 1−3; PC,VC, DMC, EMC, DMS, n = 1) were built to investigate theeffect of explicit molecules on the ring-opening reaction of ES.The results show that the electron affinity of the clustersmonotonously decreases with the number of EC moleculeincreasing from 1 to 3, while it can be facilitated bycooperating with linear molecules and VC. Linear electrolytemolecules cannot produce an effective SEI film by themselvesand inhibit the formation of SEI by increasing the ring-openingbarrier of ES. The ring-opening rate constant was alsocalculated to describe the reactivity of the clusters.Termination reactions followed by the radical anion ofLi+(ES)− and (ES)−Li+(EC) are systematically analyzed,which is able to synergistically yield the SEI layer on graphiteelectrodes.

2. COMPUTATIONAL DETAILS

All of the calculations were carried out using the Gaussian 09package.28 The equilibrium and transition structures were fullyoptimized by the B3PW91 method,29−32 using the triple splitvalence basis set 6-311G along with a set of d, p polarizationfunctions on heavy atoms and hydrogen atoms.33 To confirmthe transition states and make zero-point energy (ZPE)corrections, frequency analyses were performed at the samelevel. Intrinsic reaction coordinate (IRC) calculations weredone to confirm whether the transition states correctly connectthe stationary points. Both the explicit and implicit solventeffects were considered. The implicit solvent effect wasaccounted for by using the polarized continuum model(PCM)34 as implemented in Gaussian 09, in which aconventional set of Pauling radii is used for all calculations.A dielectric constant of EC (89.6) was used for all PCMcalculations. The specific solvent molecules were explicitlyincluded in the calculations using the clusters (ES)Li+(M)n(M: EC, n = 1−3; PC, VC, DMC, EMC, DMS, n = 1).

3. RESULTS AND DISCUSSION3.1. Reductive Activity of ES, EC, Li+(ES), Li+(EC), and

(ES)Li+(EC). The calculated binding energy (ΔEb), verticalelectron affinity (ΔE), and frontier molecular orbital energy(LUMO) of ES and EC are shown in Figure 1. Both ES and

EC can be associated with lithium ion by the oxygen of sulfoand carbonyl groups, spontaneously. The lowest ΔEb ofLi+(EC) (−47.32 kcal/mol) indicates that it is the most stableassociation form among the calculated compounds, followedby (ES)Li+(EC) and Li+(ES), which is consistent with thebond length increasing trend of Li+-ES (1.971 Å) < Li+-EC(1.869 Å) (shown in Figure 2). The lowest unoccupied

molecular orbital (LUMO) of the isolated solvent moleculeand vertical electron affinity (ΔE) are valuable descriptors forelectrolyte reductive stability.25 The LUMO energy state of ES(−1.05 eV) is much lower than that of EC (−0.35 eV). ΔE ofthe calculated for ms is as follows: Li+(ES) (−144.15 kcal/mol) > (ES)Li+(EC) (−117.88 kcal/mol) > Li+(EC) (−92.37kcal/mol) > ES (−30.03 kcal/mol) > EC (6.98 kcal/mol).These results indicate that ES can be reduced prior to EC toform a radical anion, especially at the effect of Li+. The positiveΔE (6.98 kcal/mol) of EC means that it is difficult to bereduced.

Figure 1. Binding energy (ΔEb), vertical electron affinity (ΔE), andthe energy level of the lowest unoccupied molecular orbital (LUMO)of the calculated compounds (in kcal/mol) calculated with B3PW91/6-311++G (d, p).

Figure 2. Potential energy profile for the reductive dissociationprocess of ES, Li+(ES), and Li+(EC). The red and black lines areobtained using B3PW91/6-311++G (d, p) and PCM- B3PW91/6-311++G (d, p), respectively.

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3.2. Ring-Opening Reduction of ES, Li+(ES), andLi+(EC) in Vacuum and Bulk Solvent. The selectedgeometrical structures of the relevant species for thedecomposition of ES, Li+(ES), and Li+(EC) are presented inFigure 2. From the spin density analysis, the unpaired electronis mainly located on the sulfur atom in intermediate 2 with acoefficient of 0.5, implying that the reduction of ES takes placeon sulfur atom. After gaining an electron, the S1−O3 bondincreases to 2.574 Å. Subsequently, intermediate 2 proceeds viaa transition state 3 to generate SO2 and CH2CHO. It is morestable in solution than in vacuum (−58.33 vs −30.03 kcal/mol), whereas the change in energy barrier is negligible (24.47kcal/mol in solvent vs 21.45 kcal/mol in vacuum). However,SO2 is not experimentally detected in ES-containing PC andEC-based electrolyte.16,22,23 There are two possible spec-ulations, one is that SO2 would go through more than oneelectron reduction process and another is that the open-chain

anion 2 is thermodynamically favorable to associate with Li+ toform intermediate 6 in the solution.26

It is necessary to take the salt effect on ES reduction reactioninto consideration due to the quite strong interaction betweenLi+ and ES. In sharp contrast, the S1−O3 bond breaks with theformation of a seven-membered ring after Li+(ES) gains thefirst electron. As a result of the inner-sphere electron-transferprocess, intermediate 6 proceeds via transition state 7 to giveradical anion 8. The ΔE is significantly decreased in solvent(−75.78 vs −144.15 kcal/mol); similarly, the ring-openingbarrier in solvent is much lower than that in vacuum (29.87 vs46.34 kcal/mol), indicating a significant solvent effect on thefirst electron reduction of Li+(ES). From the NBO analysis, theunpaired electron totally transfers from the sulfur atom ofintermediate 6 to the C5 atom of radical anion 8 with acoefficient of 0.99 (collected in Table 1). The electron-transferprocess is accompanied by the ring-opening reaction. The

Table 1. Relative Energy, Enthalpy, and Free Energy (in kcal/mol) of the Stationary Points, Spin Density (sd) for the SpecificAtoms, Charge (q/e) of the Lithium Atoms, and the Imaginary Frequency (ω in cm−1) of the Ring-Opening Transition Statesfor ES, Li+(ES), and Li+(EC) at PCM-B3PW91/6-311++G (d, p)a

sd

structure ΔE + ΔZPE ΔH ΔG q S1/C1 C5 ω

ES1 0.00 0.00 0.00 1.72 02 −58.33 (−33.03) −57.45 −60.70 (−34.34) 0.94 0.503TS −33.86 (−11.58) −32.45 −37.48 (−12.42) 1.11 0.55 −879.37 (−615.89)4 −78.73 (−13.60) −76.87 −85.91 (−14.46) 1.14 0.50

Li+(ES)5 0.00 0.00 0.00 0.974 06 −75.78 (−144.15) −74.98 −77.2 0 (−144.93) 0.962 0.627TS −48.73 (−97.81) −47.93 −49.96 (−98.38) 0.956 0.53 −930.38 (−1015.94)8 −78.60 (−131.36) −77.54 −79.99 (−132.21) 0.938 0.01 0.99

Li+(EC)9 0.00 0.00 0.00 0.989 010 −42.57 (−92.37) −42.72 −42.03 (−91.76) 0.947 0.8911TS −33.20 (−81.47) −33.20 −33.10 (−80.85) 0.943 0.66 0.41 −901.01 (−898.97)12 −72.45 (−120.13) −71.65 −73.27 (−120.93) 0.964 0.01 1.1

aData in parentheses refer to those in the gas phase.

Figure 3. Termination reactions of the radical anion 8 obtained using PCM-B3PW91/6-311++G (d, p).

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transition state has been confirmed by IRC calculation andfrequency analysis. The imaginary frequency of C5−O3cleavage in the TS7 locates at −930.38 cm−1 in vacuum andbecomes more negative in solvent (−1015.94 cm−1). Differ-ently, Li+−O3 bond can be formed directly after Li+(EC) getsan electron. Intermediate 10 yields radical anion 12 viatransition state 11 with a lower energy barrier (10.90 kcal/molin vacuum and 9.37 kcal/mol in solvent).3.3. Termination Reactions of the Radical Anion 8.

Termination reactions of the radical anion 8 would take placeeither by dimerization or by reacting with other involvedspecies such as intermediates and reactants (devoted in Figure3). The barrierless polymerization occurs by C5 in radicalanion 8, yielding (LiO2SOCH2CH2)2 13 (path A). A similardimerization occurs between radical anions 8 and 12,generating LiO2SO(CH2)4OCO2Li 14 (path B). The Gibbsfree energy change (ΔG) of the former reaction in solvent is1.7 kcal/mol higher than that of the latter one (−74.8 vs −73.1kcal/mol). A more stable circular dimer 14 can be formed bythe polymerization of C5 and the aggregation via intermo-lecular interactions between Li+ and O (path C), and thecorresponding ΔG is −80.9 kcal/mol in solvent. Thedimerization of lithium alkyl carbonates aggregate to eight-membered ring species (dimer, trimer, etc.) via intermolecularinteractions between Li+ and O is thermodynamicallyfavorable, which has been proved in former studies.35,36 Insolution, the first solvation shell of the radical anion 8 isaccepted to be dominated by Li+(EC). Therefore, the Li−Ccarbides would be formed by the bond formation between C5in radical anion 8 and Li+ in the Li+(EC) with lower ΔG(−83.3 kcal/mol) (path D). Moreover, O2 and O4 in radicalanion 8 cooperate with Li+ in the Li+(EC), generating lithiumalkyl sulfite (EC-Li2SO3-CH2CH2) 17 (path E), and a morestable form (ES-Li2SO3-CH2CH2) 18 can be achieved via ECreplaced by ES (path F) (−98.9 vs −93.5 kcal/mol). Inaddition, the radical anion 12 can also react with radical anion8, generating Li2CO3-ES and ethylene gas (path G) with thesecond C−O bond cleavage. It means that the ability of radicalanion 12 to get the second electron is stronger than that of 8.This observation is well consistent with the former researchthat the first and second lithium atom addition reactions to themolecules are in the order of ES > EC > PC and PC > EC >ES, respectively.37 In the one-electron reduction mechanism,Li+(ES) decomposes into ethylene and (LiSO3)

− via TS21 bythe second C6−O4 bond cleavage with a lower barrier of 13.4

kcal/mol (path I). This result is in line with the frequencyanalysis that the C6−O4 cleavage takes place at a smallervibration frequency (−490.27 cm−1 in solvent collected inTable 2). (LiSO3)

− can act as a good nucleophilic agent andreact with other species, forming the organic component of SEIor insoluble inorganic Li2SO3. However, the most favorabletermination reaction is that radical anion 8 gets the secondelectron and combines with free Li+ ion, yielding lithium sulfiteand ethylene with the most negative ΔG (−137.7 and −224.9kcal/mol in solvent and vacuum, respectively) (path H).Exper imenta l ly , Dahn et a l . 22 , 2 3 assembled Li -Ni1/3Mn1/3Co1/3O2 (NMC)/graphite pouch cells, using ESas electrolyte additive; a vigorous reactivity is observed due tothe preferential reduction of ES that also generates largeamounts of gas. It has been confirmed that ethylene is the maincomponent of the gas and Li2SO3 is the main inorganic sulfur-containing species in the SEI layer.

3.4. Solvation Reaction of Li+ in ES-Containing EC-Based Electrolyte. Though the polarized continuum modeladequately describes reactions in solution, the fact is that quitea strong interaction exists between Li+ and EC as well as ES;hence, it is necessary to take explicit molecular EC intoconsideration. Figure 4 shows the optimized structures for(ES)mLi

+(EC)n (m = 0, 1 and n = 0−4) using PCM-B3PW91/6-311++G (d, p) method. It is clear that the solvation reactiontakes place via Li+ bonds with the oxygen of sulfo or carbonylgroup. All solvation structures other than Li+(EC)4 and

Table 2. Relative Energy, Enthalpy, and Free Energy (in kcal/mol) of the Stationary Points, Spin Density (sd) for the SpecificAtoms, Charge (q/e) of the Lithium Atoms, and the Imaginary Frequency (ω in cm−1) of the Ring-Opening Transition Statesat PCM-B3PW91/6-311++G (d, p)a

sd

structure ΔE + ΔZPE ΔH ΔG S1 C5 q ω

13 −84.78 (−80.28) −84.96 −74.84 (−69.39) 0.95314 −84.82 (−80.72) −85.49 −73.07 (−68.50) 0.95315 −93.85 (−120.69) −94.47 −80.96 (−106.09) 0.96116 −93.53 (−142.28) −92.41 −83.32 (−132.53) 0.91317 −105.37 (−167.15) −104.80 −93.52 (−155.60) 0.89918 −107.21 (−173.77) −106.49 −98.09 (162.05) 0.65119 −59.48 (−70.25) −58.95 −53.75 (−62.56) 0.53420 −144.31 (−228.73) −145.29 −137.68 (−224.93) 0.91721TS −65.18 (−116.57) −63.83 −69.97 (−118.56) 0.01 1.05 0.953 −503.45 (−490.27)22 −83.13 (−130.39) −81.00 −90.60 (−132.76) 0.00 1.04 0.964

aData in parentheses refer to those in the gas phase.

Figure 4. Solvation structures of (a) Li+(EC)n, n = 1−4 and (b)(ES)Li+(EC)n, n = 0−3.

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(ES)Li+(EC)3 maintain a planar structure, and (ES)Li+(EC)3and Li+(EC)4 keep a quasi-tetrahedron. Such a structuraltransition from quasi-tetrahedron to a planar one defines thefinal state of Li+ ion intercalation into graphite. The averageLi+−O bond length, binding energy, enthalpy, Gibbs freeenergy, and the atomic charge on Li+ of the clusters(ES)mLi

+(EC)n (m = 0, 1 and n = 0−4) are collected inTable 3. The binding energy rapidly decreases with an increase

in the number of EC molecule, which is accompanied by theincrease in the average distance between lithium and oxygen. Itcan be probably attributed to the repulsion among cooperatedmolecules, which has been already proposed in the PCsolvent.26,36,38 The distance between lithium and sulfonyloxygen is longer than that between lithium and carbonyloxygen. It is probably due to the amount of the chargedistribution around sulfonyl oxygen, which is smaller than thatof carbonyl oxygen, resulting in a weaker interaction betweenlithium and sulfonyl oxygen.It is accepted that the solvation and desolvation properties

are crucial to the diffusion of Li at the interphase and thereactivity of electrolyte molecules to form SEI.39−41 O’Dwyeret al.42 have studied the solvation and desolvation properties ofLi+ ion in PC and EC electrolytes, which shows that themaximum numbers of molecule cooperating with lithium forEC and PC are four and three, respectively. This result is alsosupported by electrospray ionization mass spectroscopy (ESI-MS).39,40,43 The solvation energy of Li+(ES) is approximately7.7 kcal/mol lower than that of Li+(EC) (39.95 vs 47.73 kcal/mol), and the bond length of Li−O increases by 0.13 Å,clarifying the weak binding nature of Li+ with ES. The Gibbsfree energy of solvation of Li+(ES) (ΔG = −32.24 kcal/mol),(ES)Li+(EC) (ΔG = −30.25 kcal/mol), (ES)Li+(EC)2 (ΔG =−14.32 kcal/mol), and (ES)Li+(EC)3 (ΔG = −6.13 kcal/mol)indicates that they are likely the major solvated lithium speciesin ES-containing electrolyte.3.5. Ring-Opening Reduction of (ES)Li+(M)n; n = 1−3.

From the reaction mechanism viewpoints, the reductionprocess of (ES)Li+(M)n (M: n = 1−2) is similar to that ofLi+(ES). Compared with implicit solvent, the effect of anexplicit EC molecule on the ring-opening reaction is notobvious (comparing Figure 5b with Figure 2 Li+(ES)). Theenergy state of intermediate 23 is 1.25 kcal/mol lower thanthat of intermediate 6 (−74.53 vs −75.78 kcal/mol); however,the ring-opening barrier (TS24) is smaller than that of thesimple Li+(ES) (26.61 vs 29.87 kcal/mol). The ΔE issignificantly decreased when the number of coordinated EC

molecule increases to 2 (−65.17 vs −75.78 kcal/mol), whereasthe ring-opening barrier of (ES)Li+(EC)2 is slightly decreased(27.51 vs 29.87 kcal/mol). All of these TS models areconfirmed by IRC calculation and frequency analysis. From theNBO analysis, the unpaired electron is totally transferred fromthe sulfur atom to the carbon atom of the terminal. It has beenproved that (ES)Li+(EC)3 is thermodynamically stable, but anEC molecule will be separated after (ES)Li+(EC)3 gets anelectron (the structural evolution is shown in Figure S1).Therefore, during the ring-opening reaction of Li+(ES), twoexplicit EC molecules should be considered at most.It is exciting that the ΔE of Li+(ES) can be greatly improved

by cooperating with VC (−85.71 vs −75.78 kcal/mol),whereas it is slightly influenced by PC (shown in Figure S2).The energy barrier of (ES)Li+(M) (M: EC, PC VC) is asfollows: Li+(ES) (29.87 kcal/mol) > (ES)Li+(VC) (27.12kcal/mol) > (ES)Li+(PC) (26.62 kcal/mol) > (ES)Li+(EC)(26.61 kcal/mol). Therefore, taking the thermodynamic andkinetic aspects into consideration, it can be concluded that VCcan greatly facilitate the ring-opening reaction of Li+(ES). Thisphenomenon can be ascribed to the fact that the reactivity ofVC is higher than that of the traditional electrolyte moleculesand cooperation occurs between ES and VC during thereduction reaction of ES.

3.6. Termination Reactions of the Radical Anion 25.The termination reactions of radical anion 25 are studied, asshown in Figure 6, and specific data are collected in Table 4.Similar to the radical anion 8, the reaction that 25 gets thesecond electron and cooperates with Li+ is still the mostthermodynamically favorable one, generating EC-Li2SO3 andethylene (path F). The ΔG becomes 11.9 kcal/mol higher thanthat of radical anion 8. Compared with path E in Figure 3, pathA yielding lithium alkyl disulfite 29 exhibits 2.7 kcal/mol lessnegative in ΔG. The C5 in radical anion 25 can also attack O4in another one, generating ethylene gas and an insolublecompound in polar organic electrolyte EC-LiO2SO-(CH2)2(OSO2Li)-EC 30 (path B). However, the significantdecrease in stability of 29 and 30 may be due to its long chain.Interestingly, (ES)Li+(EC) can be induced to a seven-membered ring through C5 nucleophilicity attacking the sulfuratom with quite a negative ΔG (−111.9 kcal/mol). Similar tointermediate 6, the seven-membered structure is highlyreactive, which would undergo further reaction. The alkylsulfide (C-S) component has also been detected by XANESspectra on the graphite anode (the peak at 2473.9 eV) whenES is used as an additive in the LiCoO2/graphite pouch cell.18

As for the C-Li carbide generation (path C), the ΔG becomesmore negative compared with 17 (−106.6 vs −83.3 kcal/mol).In the one-electron reduction mechanism of (ES)Li+(EC), the

Table 3. Average Li+−O Distance (r, Å), Binding Energy(Eb, kcal/mol), Heat of Reaction (ΔH, kcal/mol), GibbsFree Energies of Reaction (ΔG, kcal/mol), and Charge onthe Li Atoms (q) at B3PW91/6-311++G (d, p)

structures r Eb ΔH ΔG q

Li+(EC) 1.756 47.32 −47.49 −41.70 0.80Li+(EC)2 1.799 36.89 −36.36 −28.30 0.85Li+(EC)3 1.876 20.99 −20.30 −13.45 0.64Li+(EC)4 1.957 12.71 −12.08 −1.98 0.54Li+(ES) 1.886 39.55 −40.22 −32.24 0.71(ES)Li+(EC) 1.811,aT 1.796 40.80 −41.15 −30.25 0.69(ES)Li+(EC)2 1.892,aT 1.872 21.55 −20.35 −14.32 0.58(ES)Li+(EC)3 1.977,aT 1.935 14.35 −13.08 −6.13 0.55

aThe bond distance between lithium and sulfonyl oxygen.

Figure 5. Potential energy profile for the reduction dissociationprocess. (a) (ES)Li+(EC)2 and (b) (ES)Li+(EC) from PCM-B3PW91/6-311++G (d, p).

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second C6−O4 bond cleavage generates ethylene and EC-(LiSO3)

− via TS33 with a barrier of 11.3 kcal/mol, which islower than that of TS21 (13.4 kcal/mol). EC-(LiSO3)

− canalso act as a good nucleophilic agent and react with otherspecies, forming the organic or inorganic species in the SEIlayer. Based on the analysis above, ethylene gas can begenerated via several paths. It may be the reason why largeamounts of ethylene gas are generated in Li -Ni1/3Mn1/3Co1/3O2/graphite pouch cells when ES is used asan additive.22 Comparing the Gibbs free energy (ΔG) of theinvolved dimerization reactions, it can be inferred that the alkylsulfide (C-S) component (32), the C-Li carbides with longchain (31), and the lithium alkyl sulfite (17, 18) are more likelyto build up an effective SEI film on the graphite anode.3.7. Ring-Opening Reaction of (ES)Li+(M) (M: DMC,

EMC, and DMS). The commonly used LIB electrolyte consistsof a mixture of linear and cyclic carbonates as solvents along

with numerous functional additives. Cyclic carbonates remainindispensable and are usually responsible for salt dissociationand SEI formation, whereas linear carbonates typically act asdiluents to render solutions less viscous and more conductiveat low temperatures.44−46 The linear molecules have a muchlower reduction potential (Li+(DMC): 0.44 V > Li+(EMC):0.44 V > Li+(DMS): 0.18 V) than that of Li+(ES), evenLi+(EC) (Supporting Information, Figure S3), clarifying thatthey would not effectively take part in the formation of the SEIlayer, especially in the presence of an electrolyte additive. Thetheoretical reduction potential of Li+(EMC) and Li+(EC) isclose to the calculation from LC-ωPBE/6-31+G (d, p)(Li+(DMC): 0.44 V, Li+(EC): 0.67 V).47 However, a quitestrong interplay exists between Li+ and cyclic molecules via thecarbonyl oxygen. In this account, the effect of linear carbonatesand sulfite on the ring-opening reduction of Li+(ES) isinvestigated in detail. All of these structures are fully optimized,

Figure 6. Termination reactions of the radical anion from the decomposition of (ES)Li+(EC) calculated with PCM-B3PW91/6-311++G (d, p).

Table 4. Relative Energy, Enthalpy, and Free Energy (in kcal/mol) of the Stationary Points, Spin Density (sd) for the SpecificAtoms, Charge (q/e) of the Lithium Atoms, and the Imaginary Frequency (ω in cm−1) of the Ring-Opening Transition Statesfor (ES)Li+(EC) and (ES)Li+(EC)2 at PCM-B3PW91/6-311++G (d, p)a

sd

structure ΔE + ΔZPE ΔH ΔG S1 C5 q ω

(ES)Li+(EC)0.00 0.00 0.00 0.930

23 −74.53 (−117.88) −74.07 −75.89(−120.82) 0.81 0.91124TS −47.92 (−76.43) −47.54 −49.17(−79.28) 0.57 0.24 0.901 −917.39 (−954.05)25 −77.23 (−108.39) −76.51 −78.56(−111.57) 0.01 1.00 0.882

(ES)Li+(EC)20.00 0.00 0.00 0.916

26 −65.17 (−90.54) −65.43 −63.63 (−90.53) 0.70 0.87827TS −37.63 (−64.96) −38.43 −34.68 (−64.50) 0.14 0.73 0.867 −993.76 (−925.96)28 −62.33 (−96.69) −62.92 −60.29 (−95.59) 0.08 1.01 0.878

Termination Reactions of the Radical Anion 2529 −84.60 (−79.50) −85.10 −72.06 (−67.13) 0.90030 −58.01 (−58.92) −56.74 −52.83 (−51.55) 0.89931 −112.29 (−123.50) −110.70 −106.59 (−110.94) 0.87332 −125.12 (−163.37) −125.19 −111.88 (−151.76) 0.90033TS −65.95 (−95.61) −65.13 −68.37 (−99.85) 0.25b 0.54b 0.894 −492.50 (−529.33)34 −77.23 (−112.20) −76.51 −78.56 (−118.65) 0.20b 0.7b 0.88235 −136.08 (−229.66) −137.91 −125.79 (−222.89) 0.900

aData in parentheses refer to those in the gas phase. bSpin density on O4 and C6 seen in Figure 6.

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as shown in Figure 7, and relevant data are collected in Table5.Differently, the ΔE of Li+(ES) can be greatly improved by

cooperating with EMC and DMC. The law of its changebetween (ES)Li+(DMC) and (ES)Li+(EMC) is similar to thatbetween (ES)Li+(EC) and (ES)Li+(PC), as the appearance ofmethyl can change the competitiveness of electrolyte moleculeto capture the electron.48,49 Unfortunately, the kinetics of thering-opening reaction of ES is significantly inhibited (energybarrier (ES)Li+(DMC): 39.9 kcal/mol, (ES)Li+(DMS): 34.1kcal/mol, and (ES)Li+(EMC): 39.8 kcal/mol). From thecalculation results, it is worth noting that the energy barrier ofLi+(ES) cooperating with linear carbonate molecule is muchlarger than itself, cooperating with a cyclic carbonate molecule.This observation is in line with the frequency analysis that thefrequency of C−O bond cleavage of the Li+(ES) cooperatingwith linear carbonates is larger than that of Li+(ES)cooperating with cyclic ones (collected in Tables 4 and 5).3.8. Rate Constant of the Ring-Opening Reaction for

(ES)Li+(M) (M: EC, PC, VC, DMC, EMC, and DMS). From

the above analysis, it can be concluded that species in theelectrolyte would take part in the reduction decomposition ofES. The electron affinity and the ring-opening energy barrier of(ES)Li+(M) are very different. Therefore, it is meaningful totake thermodynamic and kinetic aspects of the ring-openingreaction into account for describing the reductive decom-position of ES in the clusters. It is necessary to deal with therate constant for the entire one-electron reduction decom-position consisting of the electrochemistry equilibrium andkinetic aspects,27,49 which is presented in Figure S4. Addition-ally, the reduction potential is calculated to estimate thereductive stability of clusters (ES)Li+(M) (M = EC, PC, VC,DMC, DMS, EMC), which subtracts 1.39 V to account for theexperimentally measured potential of the reference electrode(Li/Li+).26,50

The calculated reduction potential (Eθ), equilibriumconstant (K), rate constant (k′), and the overall rate constant(k) are collected in Table 6. The one-electron reductionpotential of the calculated forms is as follows: (ES)Li+(VC)(2.33 V) > (ES)Li+(EMC) (2.11 V) > (ES)Li+(DMC) (2.00

Figure 7. Potential energy profile for the reductive dissociation process of (ES)Li+(DMC), (ES)Li+(DMS), and (ES)Li+(EMC) from PCM-B3PW91/6-311++G (d, p).

Table 5. Relative Energy, Enthalpy, and Free Energy (in kcal/mol) of the Stationary Points, Spin Density (sd) for the SpecificAtoms, Charge (q/e) of the Lithium Atoms, and the Imaginary Frequency (ω in cm−1) of the Ring-Opening Transition Statesfor (ES)Li+(EMC), (ES)Li+(DMS), and (ES)Li+(DMC) at PCM-B3PW91/6-311++G (d, p)a

sd

structure ΔE + ΔZPE ΔH ΔG S1/C1 C5 q ω

(ES)Li+(DMC)36 0.00 0.00 0.00 0.95837 −81.93 (−109.46) −83.15 −78.38 (−108.50) 0.61 0.86138TS −42.15 (−67.06) −43.39 −38.33 (−66.13) 0.23 0.68 0.862 −1008.58 (−965.54)39 −72.22 (−100.45) −73.09 −68.82 (−99.64) 0.01 0.96 0.847

(ES)Li+(DMS)40 0.00 0.00 0.00 0.95341 −75.61 (−115.82) −74.17 −77.94 (−115.56) 0.48 0.89642TS −41.52 (−81.91) −40.59 −41.51 (−80.53) 0.26 0.55 0.855 −968.74 (−659.25)43 −71.82 (−110.30) −70.33 −72.90 (−109.31) 0 0.71 0.884

(ES)Li+(EMC)44 0.00 0.00 0.00 0.97445 −83.50 (−111.48) −84.72 −81.24 (−110.93) 0.71 0.86046TS −43.66 (−69.03) −44.38 −42.81 (−68.26) 0.26 0.46 0.862 −1005.30 (−962.90)47 −72.90 (−102.46) −73.83 −70.69 (−101.89) 0.00 0.91 0.846

aData in parentheses refer to those in the gas phase.

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V) > (ES)Li+(DMS) (1.98 V) > Li+(ES) (1.94 V) >(ES)Li+(EC) (1.89 V) > (ES)Li+(PC) (1.88 V), which agreeswell with the experimental data (1.9−2.1 V) in the literature.16

Compared with the clusters in consideration, the smallestequilibrium constant K (3.15 × 1044) and a rather small k′result in the smallest k for the reductive decomposition of ES,forming SO2 and aldehyde (2.47 × 1035 s−1), which explainwhy the SO2 is not detected in the experiment. Additionally,the equilibrium constant for the formation of intermediate(ES)−Li+(M) of the clusters is very different, which issignificantly inhibited by cooperating with EC and PC((ES)−Li+(EC): 4.34 × 1055, (ES)−Li+(PC): 2.43 × 1055),whereas it can be increased by cooperating with the linearelectrolyte molecules ((ES)−Li+(DMC): 2.86 × 1057,(ES)−Li+(EMC): 3.62 × 1059, (ES)−Li+(DMS): 1.37 ×1057). Taking the thermodynamic and kinetic aspects togetherto describe the ring-opening reaction, the overall rate constantis listed as follows: (ES)Li+(PC) (9.21 × 1047 s−1) > Li+(ES)(8.47 × 1047 s−1) > (ES)Li+(EC) (7.07 × 1047 s−1) >(ES)Li+(DMS) (3.11 × 1043 s−1) > (ES)Li+(EMC) (1.91 ×1041 s−1) > (ES)Li+(DMC) (2.48 × 1037 s−1) > ES (2.47 ×1035 s−1). It suggests that the overall rate constant of the ring-opening reaction can be seriously inhibited by the linearelectrolyte molecules while it maintains the same level bycooperating with PC and EC. Therefore, we propose that thelinear electrolyte molecules not only cannot produce effectiveSEI film by themselves but also cannot inhibit the formation ofSEI by increasing the ring-opening barrier of ES. It is worthnoticing that both K (1.39 × 1063) and k′ (2.94 × 10−8 s−1) areimproved by cooperating with VC, leading to the largestoverall rate constant (k: 4.09 × 1055 s−1) of the ring-openingreaction for (ES)Li+(VC) among all species.

4. CONCLUSIONSIn this work, we provide a comprehensive understanding of thereduction mechanism of ES in EC-based electrolyte by thedensity function theory (B3PW91) calculations. The clusters(ES)Li+(M)n (M: EC, n = 1−3; PC, VC, DMC, EMC, DMS, n= 1) are built to investigate the effect of explicit solventmolecules on the ring-opening reaction of ES. The resultssuggest that the electron affinity of Li+(ES) is inhibited aftercooperating with cycle carbonates (EC and PC) while beingfacilitated by cooperating with cosolvents (DMC, EMC, andDMS). However, the calculation of the kinetics shows that thering-opening reaction of Li+(ES) is seriously inhibited bycooperating with cosolvents. Herein, we propose that thecosolvents not only cannot take part but also cannot inhibit theformation of SEI by increasing the ring-opening barrier of ES.

It is interesting that the thermodynamics and kinetics of thering-opening reduction of Li+(ES) can be significantlyfacilitated by cooperating with VC (K: (ES)Li+(VC): 1.39 ×1063 vs Li+(ES): 3.92 × 1056; k′: (ES)Li+(VC): 4.09 × 1055 vsLi+(ES): 2.16 × 10−9 s−1). The theoretical reduction potentialof the (ES)Li+(M) agrees well with the experimental one(1.8−2.1 V). The second-electron reduction of ES formingLi2SO3 and ethylene gas is the most thermodynamic favorablereaction. The alkyl sulfide (C-S) component (32), the C-Licarbides, and the lithium alkyl sulfite ((CH2CH2OS2Li)2,LiO2CO(CH2)4OSO2Li, etc.) formed by the terminationreactions of the radical anions 8 and 25 are able to build upan effective SEI layer on the anode of LIBs.

■ ASSOCIATED CONTENT

*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.jpcc.8b12000.

Structural evolution before/after (ES)Li+(EC)3 gets anelectron, potential energy profile of the reductivedissociation process of (ES)Li+(VC) and (ES)Li+(PC),the reduction potential and solvation energy of Li+(EC)Li+(DMC), Li+(EMC), and Li+(DMS), and thethermodynamic and kinetic steps of the ring-openingreaction of (ES)Li+(M) (PDF)

■ AUTHOR INFORMATION

Corresponding Author*E-mail: [email protected].

ORCIDFucheng Ren: 0000-0001-7078-6238Shiyao Zheng: 0000-0001-5002-5204NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was financially supported by the National NaturalScience Foundation of China (grant nos. 21761132030,21621091, and 21473148).

■ REFERENCES(1) Jansen, A.; Kahaian, A.; Kepler, K.; Nelson, P.; Amine, K.; Dees,D.; Vissers, D.; Thackeray, M. Development of a High-PowerLithium-Ion Battery. J. Power Sources 1999, 81−82, 902−905.(2) Scrosati, B. Recent Advances in Lithium Ion Battery Materials.Electrochim. Acta 2000, 45, 2461−2466.(3) Scrosati, B. History of Lithium Batteries. J. Solid StateElectrochem. 2011, 15, 1623−1630.(4) Megahed, S.; Ebner, W. Lithium-Ion Battery for ElectronicApplications. J. Power Sources 1995, 54, 155−162.(5) Tarascon, J.-M.; Armand, M. Issues and Challenges FacingRechargeable Lithium Batteries. Materials for Sustainable Energy: ACollection of Peer-Reviewed Research and Review Articles from NaturePublishing Group; World Scientific, 2011; pp 171−179.(6) Lu, L.; Han, X.; Li, J.; Hua, J.; Ouyang, M. A Review on the KeyIssues for Lithium-Ion Battery Management in Electric Vehicles. J.Power Sources 2013, 226, 272−288.(7) Barre, A.; Deguilhem, B.; Grolleau, S.; Gerard, M.; Suard, F.;Riu, D. A Review on Lithium-Ion Battery Ageing Mechanisms andEstimations for Automotive Applications. J. Power Sources 2013, 241,680−689.

Table 6. Reduction Potential (Eθ/V), Equilibrium ConstantK for the Reduction (ES)Li+(M), Kinetic Rate Constant k′for the Ring Opening of ES, and the Overall Rate Constantk at T = 298.15 K

Eθ K k′ (s−1) k (s−1)

ES 2.32 3.15 × 1044 7.84 × 10−10 2.47 × 1035

Li+(ES) 1.94 3.92 × 1056 2.16 × 10−9 8.47 × 1047

(ES)Li+(EC) 1.89 4.34 × 1055 1.63 × 10−8 7.07 × 1047

(ES)Li+(VC) 2.33 1.39 × 1063 2.94 × 10−8 4.09 × 1055

(ES)Li+(PC) 1.88 2.43 × 1055 3.79 × 10−8 9.21 × 1047

(ES)Li+(DMC) 2.00 2.86 × 1057 8.68 × 10−20 2.48 × 1037

(ES)Li+(EMC) 2.11 3.62 × 1059 5.28 × 10−19 1.91 × 1041

(ES)Li+(DMS) 1.98 1.37 × 1057 2.27 × 10−14 3.11 × 1043

The Journal of Physical Chemistry C Article

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Page 9: Comprehensive Understanding of Reduction Mechanisms of ... · Comprehensive Understanding of Reduction Mechanisms of ... followed by dimerization reaction and/or the second-electron

(8) Wang, A.; Kadam, S.; Li, H.; Shi, S.; Qi, Y. Review on Modelingof the Anode Solid Electrolyte Interphase (SEI) for Lithium-IonBatteries. npj Comput. Mater. 2018, 4, 15.(9) Zhang, S. S. A Review on Electrolyte Additives for Lithium-IonBatteries. J. Power Sources 2006, 162, 1379−1394.(10) Xu, K. Nonaqueous Liquid Electrolytes for Lithium-BasedRechargeable Batteries. Chem. Rev. 2004, 104, 4303−4418.(11) Abe, K.; Yoshitake, H.; Kitakura, T.; Hattori, T.; Wang, H.;Yoshio, M. Additives-Containing Functional Electrolytes for Sup-pressing Electrolyte Decomposition in Lithium-Ion Batteries. Electro-chim. Acta 2004, 49, 4613−4622.(12) Zuo, X.; Fan, C.; Xiao, X.; Liu, J.; Nan, J. MethyleneMethanedisulfonate as an Electrolyte Additive for Improving theCycling Performance of LiNi0.5Co0.2Mn0.3O2/Graphite Batteries at 4.4V Charge Cutoff Voltage. ECS Electrochem. Lett. 2012, 1, A50−A53.(13) Xia, J.; Sinha, N.; Chen, L.; Kim, G.; Xiong, D.; Dahn, J. Studyof Methylene Methanedisulfonate as an Additive for Li-Ion Cells. J.Electrochem. Soc. 2014, 161, A84−A88.(14) Janssen, P.; Schmitz, R.; Muller, R.; Isken, P.; Lex-Balducci, A.;Schreiner, C.; Winter, M.; Cekic-Laskovic, I.; Schmitz, R. 1, 3, 2-Dioxathiolane-2, 2-Dioxide as Film-Forming Agent for PropyleneCarbonate Based Electrolytes for Lithium-Ion Batteries. Electrochim.Acta 2014, 125, 101−106.(15) Wu, Z.; Li, S.; Zheng, Y.; Zhang, Z.; Umesh, E.; Zheng, B.;Zheng, X.; Yang, Y. The Roles of Sulfur-Containing Additives andTheir Working Mechanism on the Temperature-Dependent Perform-ances of Li-Ion Batteries. J. Electrochem. Soc. 2018, 165, A2792−A2800.(16) Wrodnigg, G. H.; Besenhard, J. O.; Winter, M. Ethylene Sulfiteas Electrolyte Additive for Lithium-Ion Cells with Graphitic Anodes. J.Electrochem. Soc. 1999, 146, 470−472.(17) Wrodnigg, G. H.; Besenhard, J. O.; Winter, M. Cyclic andAcyclic Sulfites: New Solvents and Electrolyte Additives for LithiumIon Batteries with Graphitic Anodes? J. Power Sources 2001, 97−98,592−594.(18) Ota, H.; Akai, T.; Namita, H.; Yamaguchi, S.; Nomura, M.XAFS and TOF−SIMS Analysis of SEI Layers on Electrodes. J. PowerSources 2003, 119−121, 567−571.(19) Jeong, S.-K.; Inaba, M.; Mogi, R.; Iriyama, Y.; Abe, T.; Ogumi,Z. Surface Film Formation on a Graphite Negative Electrode inLithium-Ion Batteries: Atomic Force Microscopy Study on the Effectsof Film-Forming Additives in Propylene Carbonate Solutions.Langmuir 2001, 17, 8281−8286.(20) Sano, A.; Maruyama, S. Decreasing the Initial IrreversibleCapacity Loss by Addition of Cyclic Sulfate as Electrolyte Additives. J.Power Sources 2009, 192, 714−718.(21) Xu, M.; Li, W.; Lucht, B. L. Effect of Propane Sultone onElevated Temperature Performance of Anode and Cathode Materialsin Lithium-Ion Batteries. J. Power Sources 2009, 193, 804−809.(22) Xia, J.; Aiken, C. P.; Ma, L.; Kim, G. Y.; Burns, J. C.; Chen, L.P.; Dahn, J. R. Combinations of Ethylene Sulfite (ES) and VinyleneCarbonate (VC) as Electrolyte Additives in LiNi1/3Mn1/3Co1/3O2/Graphite Pouch Cells. J. Electrochem. Soc. 2014, 161, A1149−A1157.(23) Madec, L.; Petibon, R.; Tasaki, K.; Xia, J.; Sun, J. P.; Hill, I. G.;Dahn, J. R. Mechanism of Action of Ethylene Sulfite and VinyleneCarbonate Electrolyte Additives in LiNi1/3Mn1/3Co1/3O2/GraphitePouch Cells: Electrochemical, GC-MS and XPS Analysis. Phys. Chem.Chem. Phys. 2015, 17, 27062−27076.(24) Madec, L.; Xia, J.; Petibon, R.; Nelson, K. J.; Sun, J. P.; Hill, I.G.; Dahn, J. R. Effect of Sulfate Electrolyte Additives onLiNi1/3Mn1/3Co1/3O2/Graphite Pouch Cell Lifetime: Correlationbetween XPS Surface Studies and Electrochemical Test Results. J.Phys. Chem. C 2014, 118, 29608−29622.(25) Xing, L.; Li, W.; Xu, M.; Li, T.; Zhou, L. The ReductiveMechanism of Ethylene Sulfite as Solid Electrolyte Interphase Film-Forming Additive for Lithium Ion Battery. J. Power Sources 2011, 196,7044−7047.(26) Leggesse, E. G.; Jiang, J. C. Theoretical Study of the ReductiveDecomposition of Ethylene Sulfite: A Film-Forming Electrolyte

Additive in Lithium Ion Batteries. J. Phys. Chem. A 2012, 116, 11025−11033.(27) Sun, Y.; Wang, Y. New Insights into the Electroreduction ofEthylene Sulfite as an Electrolyte Additive for Facilitating SolidElectrolyte Interphase Formation in Lithium Ion Batteries. Phys.Chem. Chem. Phys. 2017, 19, 6861−6870.(28) Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.;Cheeseman, J.; Montgomery, J., Jr.; Vreven, T.; Kudin, K.; Burant, J.Gaussian 03, revision C 02; Gaussian, Inc.: Wallingford, CT, 2004;Vol. 26.(29) Becke, A. D. Density-Functional Thermochemistry. Iii. TheRole of Exact Exchange. J. Chem. Phys. 1993, 98, 5648−5652.(30) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized GradientApproximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865.(31) Burke, K.; Perdew, J. P.; Wang, Y. Derivation of a GeneralizedGradient Approximation: The PW91 Density Functional. ElectronicDensity Functional Theory; Springer, 1998; pp 81−111.(32) Perdew, J. P.; Burke, K.; Wang, Y. Generalized GradientApproximation for the Exchange-Correlation Hole of a Many-Electron System. Phys. Rev. B: Condens. Matter Mater. Phys. 1996,54, 16533.(33) Frisch, M. J.; Pople, J. A.; Binkley, J. S. Self-ConsistentMolecular Orbital Methods 25. Supplementary Functions forGaussian Basis Sets. J. Chem. Phys. 1984, 80, 3265−3269.(34) Barone, V.; Cossi, M. Quantum Calculation of MolecularEnergies and Energy Gradients in Solution by a Conductor SolventModel. J. Phys. Chem. A 1998, 102, 1995−2001.(35) Matsuta, S.; Asada, T.; Kitaura, K. Vibrational Assignments ofLithium Alkyl Carbonate and Lithium Alkoxide in the InfraredSpectra an Ab Initio Mo Study. J. Electrochem. Soc. 2000, 147, 1695−1702.(36) Wang, Y.; Nakamura, S.; Tasaki, K.; Balbuena, P. B. TheoreticalStudies to Understand Surface Chemistry on Carbon Anodes forLithium-Ion Batteries: How Does Vinylene Carbonate Play Its Role asan Electrolyte Additive? J. Am. Chem. Soc. 2002, 124, 4408−4421.(37) Han, Y. K.; Lee, S. U.; Ok, J. H.; Cho, J. J.; Kim, H. J.Theoretical Studies of the Solvent Decomposition by Lithium Atomsin Lithium-Ion Battery Electrolyte. Chem. Phys. Lett. 2002, 360, 359−366.(38) Wang, Y.; Balbuena, P. B. Theoretical Insights into theReductive Decompositions of Propylene Carbonate and VinyleneCarbonate: Density Functional Theory Studies. J. Phys. Chem. B 2002,106, 4486−4495.(39) Fukushima, T.; Matsuda, Y.; Hashimoto, H.; Arakawa, R.Studies on Solvation of Lithium Ions in Organic Electrolyte Solutionsby Electrospray Ionization-Mass Spectroscopy. Electrochem. Solid-StateLett. 2001, 4, A127−A128.(40) Fukushima, T.; Matsuda, Y.; Hashimoto, H.; Arakawa, R.Solvation of Lithium Ions in Organic Electrolytes of Primary LithiumBatteries by Electrospray Ionization-Mass Spectroscopy. J. PowerSources 2002, 110, 34−37.(41) Xu, K.; von Cresce, A.; Lee, U. Differentiating Contributions to“Ion Transfer” Barrier from Interphasial Resistance and Li+ Desolva-tion at Electrolyte/Graphite Interface. Langmuir 2010, 26, 11538−11543.(42) Bhatt, M. D.; O’Dwyer, C. The Role of Carbonate and SulfiteAdditives in Propylene Carbonate-Based Electrolytes on theFormation of Sei Layers at Graphitic Li-Ion Battery Anodes. J.Electrochem. Soc. 2014, 161, A1415−A1421.(43) Matsuda, Y.; Fukushima, T.; Hashimoto, H.; Arakawa, R.Solvation of Lithium Ions in Mixed Organic Electrolyte Solutions byElectrospray Ionization Mass Spectroscopy. J. Electrochem. Soc. 2002,149, A1045−A1048.(44) Borodin, O.; Ren, X.; Vatamanu, J.; von Wald Cresce, A.; Knap,J.; Xu, K. Modeling Insight into Battery Electrolyte ElectrochemicalStability and Interfacial Structure. Acc. Chem. Res. 2017, 50, 2886−2894.(45) Xu, K. Electrolytes and Interphases in Li-Ion Batteries andBeyond. Chem. Rev. 2014, 114, 11503−11618.

The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.8b12000J. Phys. Chem. C 2019, 123, 5871−5880

5879

Page 10: Comprehensive Understanding of Reduction Mechanisms of ... · Comprehensive Understanding of Reduction Mechanisms of ... followed by dimerization reaction and/or the second-electron

(46) Ue, M.; Sasaki, Y.; Tanaka, Y.; Morita, M. NonaqueousElectrolytes with Advances in Solvents. Electrolytes for Lithium andLithium-Ion Batteries; Springer, 2014; pp 93−165.(47) Borodin, O.; Olguin, M.; Spear, C. E.; Leiter, K. W.; Knap, J.Towards High Throughput Screening of Electrochemical Stability ofBattery Electrolytes. Nanotechnology 2015, 26, No. 354003.(48) Xing, L.; Zheng, X.; Schroeder, M.; Alvarado, J.; von WaldCresce, A.; Xu, K.; Li, Q.; Li, W. Deciphering the EthyleneCarbonate−Propylene Carbonate Mystery in Li-Ion Batteries. Acc.Chem. Res. 2018, 51, 282−289.(49) McQuarrie, D. A.; Cox, H.; Simon, J. D. Physical Chemistry: AMolecular Approach; Sterling Publishing Company, 1997.(50) Trasatti, S. The absolute electrode potential: an explanatorynote (Recommendations 1986). Pure Appl. Chem. 1986, 58, 955−966.

The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.8b12000J. Phys. Chem. C 2019, 123, 5871−5880

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